1. Field of the Invention
The present invention relates to an optical device, in particular for a motor vehicle, such as a lighting and/or indicating device having in particular a photometric function that is useful when the vehicle is moving on the road, allowing the vehicle to be seen by other vehicles or allowing the driver of the vehicle to see outside.
2. Description of the Related Art
The use of surface light sources as light source of a motor vehicle optical device, in particular an organic light-emitting diode, also called an OLED, is known, in particular from document DE 10 2007 018 985, which document is incorporated herein by reference and made a part hereof. In the case of DE 10 2007 018 985, which is incorporated herein by reference and made a part hereof, the motor vehicle optical device is an indicating device for a motor vehicle. Although an extremely homogeneous light can be provided by an organic light-emitting diode type light source, it has a number of drawbacks:                First, organic light-emitting diodes today comprise small molecules, since they are the most efficient and more suited to producing an indicating function in a limited space, for example a vehicle rear wing. However, these molecules must be protected from water and oxygen molecules, and this is achieved using glass plates. Organic light-emitting diodes used to perform an indicating function therefore comprise a protective glass plate in contact with the emitting layer. The glass plates highly restrict the possible shapes of the organic light-emitting diodes. The organic light-emitting diodes must therefore have flat surfaces or at most ruled surfaces, and they must therefore not consist of a screen having any kind of warped surface such as the usual glass plate of an optical device for a motor vehicle. This therefore raises design issues.        Next, the luminance provided by an organic light-emitting diode of present-day technology is not sufficient to provide certain indicating functions (such as “city light”, “stop lamp” and “center high mount stop lamp” indicating functions). An organic light-emitting diode of present-day technology typically provides a luminance of 1,000 Cd/m2, while to fulfill the abovementioned functions, a luminance of 5,000 to 10,000 Cd/m2 would be necessary. Nevertheless, a new technology of organic light-emitting diodes provides for markedly increasing the directivity of emission of the diode in the direction perpendicular to its emitting surface. Thus, without increasing the emittance of the diode, the luminance can be increased strongly, for example by a factor of 10, to reach about 10,000 Cd/m2. However, an organic light-emitting diode of this technology is very directional. Consequently, it exhibits, in addition to the drawback mentioned previously, the drawback of having to be oriented in the longitudinal axis of the vehicle or more generally in the direction toward which it must emit light. This therefore raises design issues, in particular issues of size and design.        
Consequently, the use of an organic light-emitting diode in a motor vehicle lighting and/or indicating device is viable only if this surface is a ruled surface. Hence, a lighting and/or indicating device can be produced by placing an organic light-emitting diode on a flexible substrate. The performance levels of such a technology are very low in comparison with technologies in which the diodes are placed on a flat glass substrate.
There is also known from document DE 10 2007 018 986, which is incorporated herein by reference and made a part hereof, a lighting device for a motor vehicle passenger compartment comprising:                a group of organic light-emitting diodes on which are bonded a first optical component, and        a second optical component.        
There is also known from documents DE 202 07 799 and EP 1 485 959, which are equivalent to U.S. Patent Publication 2005/0117347, which documents are incorporated herein by reference and made a part hereof, motor vehicle indicating devices comprising an organic light-emitting diode covered by an optical component comprising a spatial repetition of a pattern with the aim of improving the performance of the diode by virtue of the fact that the rays are less easily trapped by total reflection and can thus more easily exit the transparent substrate. This technology makes sense only if the optical component is bonded to the substrate, or in other words if the optical component is bonded to a plane. Such indicating devices do not provide for solving the problems mentioned earlier.
There is also known from document FR 2 926 677, which is equivalent to U.S. Patent Publication 2011/0079722, which documents are incorporated herein by reference and made a part hereof, an organic light-emitting diode device emitting a light beam exhibiting high directivity. Such an organic light-emitting diode comprises, between these two electrodes, various layers, in particular a light-emitting layer, a layer encouraging the transport of electrons up to the emitting layer and a layer encouraging the transport of holes up to the emitting layer. All these layers form a microcavity, the thickness of which is adjusted to create an optical resonance. The result of such a structure is an emission of a light beam exhibiting high directivity.
What is needed, therefore, is an optical device that overcomes one or more of the above-mentioned problems in the prior art.